Veggie mushroom burger An irresistible vegetarian mushroom burger filled with melty mozzarella and slathered in homemade tomato relish. This is designed to be a low cost recipe. Ingredients For the relish 1 tbsp olive oil 1 onion, finely diced salt and pepper 1 garlic clove, crushed 200g/7oz tinned tomatoes 1 tbsp white wine vinegar For the onions 25g/1oz butter 2 onions, finely sliced For the rest of the burger 4 large flat mushrooms, stalk trimmed so it doesn’t come above the edge of the mushroom 1 tbsp olive oil 1 ball mozzarella 4 burger buns, sliced in half Recipe tips Method Preheat the oven to 180C/160C Fan/Gas 4. For the relish, heat a small frying pan over a medium heat and add the olive oil. Fry the onion and a pinch of salt in the oil for 4-5 minutes, or until the onion is soft. Add the garlic and cook for two minutes, then stir in the tomatoes and the vinegar. Gently simmer for five minutes, or until the mixt...